<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>class选择器</title>

    <style> 
        .c1{
            width: auto;
            height: 150px;
            background-color: antiquewhite;
        }
        .c2{
            width: 65%;
            height: 130px;
            background-color: aquamarine;
        }
    </style>
</head>
<body>
    <div class="c1">
        class1
    </div>
    <div class="c1 c2">
        class2
    </div>
</body>
</html>